A variety of suspension systems for folding doors and curtains are known. Such systems suspend the curtain or folding door in a hung position, and include means for opening and closing the curtain or door by movement of the suspension system in an essentially horizontal direction. In general, the design of such overhead suspension systems varies with the intended application, particularly the size and weight of the curtain or folding door. For example, a simple shower curtain can be suspended from a horizontal bar by a series of sliding hooks or loops. See, for example, Strebeigh U.S. Pat. No. 3,035,275 issued May 22, 1962, and Boerner U.S. Pat. No. 3,321,003 issued May 23, 1967. For heavier doors or curtains, more elaborate hanging systems, e.g. traverse rods, have been proposed.
Industrial doors comprising a series of adjacent flexible plastic strips suspended from a doorway are generally known. See, for example, Catan U.S. Pat. No. 4,289,190 issued Sept. 15, 1981, Barbant U.S. Pat. No. 4,449,270 issued May 22, 1984, Schaefer U.S. Pat. No. 4,388,961 issued June 21, 1983, Romano U.S. Pat. No. 4,355,678 issued Oct. 26, 1982, Simon U.S. Pat. No. 4,335,777 issued June 22, 1982, and Sills U.K. Patent Application No. 2,080,379 published Feb. 3, 1982.
For industrial doors including a series of overlapping strips or hinged sections which draw to one side in a fan-folded position, typical suspension systems include a series of rack sections connected to each corresponding section of the curtain or door secured to suitable means for effecting a fan-fold opening and closing movement. Each rack section can be connected to an overhead guide track by a series of pins pivotally connected to rollers, as illustrated by Romano U.S. Pat. No. 4,083,395 issued Apr. 11, 1978. In lieu of rollers, simple sliding support devices can be employed, such as described in Sandall U.K. Patent Specification No. 1,554,159 published Oct. 17, 1979. The wheels or support devices are typically interlocked with the guide track. Comeau U.S. Pat. No. 4,274,467 fold type drapery suspension system.
One known design for an industrial door of the strip type combines the advantages of an overhead suspension system including a series of hinged, fan-foldable rack sections with a means for automatically opening and closing the door. The present inventor proposed such a system in German Patent No. 3,048,763 published Sept. 6, 1983, the features of which are illustrated in FIGS. 1, 2 and 3 of the present application. The entire contents of the German Patent No. 3,048,763 are hereby expressly incorporated herein by reference.
As shown in FIGS. 1-3, a known folding door includes a series of flexible transparent strips 1 having overlapping edge portions 1A each attached to a rack 3 consisting of jointed sections 4, 5 and 6 which can be folded along a guide track 7. Section 4 located nearest the doorway edge is linked to a bearing bolt 9 below guide track 7. The free end 4A of rack section 4 is joined to a second rack section 5 of double length which is attached at its center by a swivel joint 10 and support rod 11 to a carriage 12 which comprises a vertically oriented plate having a series of rollers 12A mounted thereon. Rollers 12A engage the inner periphery of guide track 7, as illustrated in FIG. 3.
Second rack section 5 has an end 5A connected to third rack section 6 which moves in parallel with first rack section 4. End portion 6A of rack section 6 is attached by a swiveling joint 13 and support rod 14 to carriage 15.
A draw cable assembly 16 and a pair of draw rods 17A, 17B are disposed above guide track 7 and are connected to support rods 14 of each rack 3. Sprocket chains 18, 19 connected to draw rods 17A, 17B are guided by sprocket wheels 20, 21, at least one of which is powered by a motor (not shown) to turn in either direction to open and close the door, respectively.
Hinge pins 23 of hinges 22 connecting respective rack sections 4, 5 and 6 are offset relative to an imaginery vertical longitudinal plane bisecting rack sections 5, 6. This allows sections 4, 5, 6 to fold parallel to each other in the manner shown in FIG. 3. Hinge connections 22 may further have spring biased studs 25 which protrude from the end of at least one of each two adjoining sections 4, 5 and 5, 6 which assist hinging by exerting pressure on abutment end surface 26 of rack section end 5A, as illustrated in FIG. 3.
The track system described above in connection with the folding door illustrated in FIGS. 1 through 3 has several shortcomings. Performance of such a door, particularly when installed at a doorway to the outdoors, suffers due to high winds or negative air pressure. Specifically, the wind or air pressure may push the door so that it hangs at an angle partially supported by the wind or air pressure, i.e. at an angle to its normal perpendicular position relative to the floor. When this happens, carriage 12, particularly rollers 12A, pivot within guide track 7, increasing friction when the door is opened and closed, in some cases jamming the door.
The foregoing known automatic door system is also quite limited in the number of frame sections which can be employed, in other words, the total length of rack 3. In general, to function smoothly, the foregoing door should have no more than about six rack sections 4, 5, 6 total, three per site, each rack section 4-6 having a length of thirty inches or less. If additional rack sections are added, or the rack sections 4-6 are lengthened beyond thirty inches, friction increases to the point where it becomes difficult to drive the suspension system between opened and closed positions.
The present invention provides a track system for a heavy duty flexible industrial door which can overcome some of the aforementioned drawbacks of known track suspension systems.